Ovarian cancer is the most lethal cancer of the female reproductive system, with over 21,000 new ovarian cancer diagnoses and 14,000 deaths annually in the US. The menstrual cycle, specifically the total lifetime number of ovulations, is a key risk factor for developing ovarian cancer. Factors that repress ovulation reduce the risk of ovarian cancer, such as oral contraceptives, pregnancy, and late menarche. The most common and deadly histotype of ovarian cancer, termed high grade serous cancer (HGSC), likely originates from the fallopian tube epithelial cells, and not the ovary. The frequent detection of tumors in the ovary, which resulted in the name ?ovarian cancer?, suggests that the ovary provides a unique anatomical location for tumor migration and expansion. Since most research supports that the fallopian tube is the source of ovarian cancer, it becomes critical to understand how ovulation contributes to tumor initiation in this site. Our team developed three-dimensional organotypic cultures supported in a state-of-the-art microfluidic platform that supports the ovary to produce dynamic hormone profiles that closely mimic the 28-day human reproductive menstrual cycle and ovulation on platform. The device was one of the C&E News Top 10 Inventions of 2017 and our paper in Nature Communications was the top NIEHS paper of 2017. The proposal will build on this successful collaboration to expand our technology and models to studying the role of the ovary in fallopian tube carcinogenesis and metastasis. Our hypothesis is that the microenvironment of the ovary contributes to tumor initiation, migration, and tumor cell expansion of high grade serous cancers derived from fallopian tube. Aim 1 will integrate our 3D culture of the ovary and models of the fallopian tube in a new PREDICT96 microfluidic device to define the how the physiological process of ovulation, specifically follicular fluid, drives fallopian tube tumor initiation using primary human fallopian tube samples, preneoplastic cell models, tumor models, and a transgenic mouse model developed in the Burdette lab. In Aim 2, we will validate the role of the secreted protein, versican, from the 3D ovary that enhances fallopian tube homing to the ovary and we will test small molecules for their ability to block ovarian colonization using 3D ex vivo microfluidic models and in vivo. In Aim 3, we will investigate the mechanisms responsible for tumor cell escape from the fallopian tube, which we hypothesize is due to spheroid formation and the colonization of exposed three- dimensional collagen in the ovary at sites of ovulation. Overall, this grant will employ unique devices, primary human tissues, and three dimensional preneoplastic and tumor models to unveil new biological targets in an effort to reduce tumor initiation and spread of fallopian derived high grade serous cancer in the ovarian microenvironment.